Refactor validators to use shared IO helpers for file access

[willwade]

Motivation

• Remove direct fs/path usage in validators to avoid React/browser warnings and to follow the repository's environment-agnostic IO conventions.
• Use the existing IO helpers and zip adapter approach so validation remains functional in both Node and browser runtimes.

Description

• Replaced direct fs/path imports and readFileSync/statSync/path.basename calls in multiple validators with readBinaryFromInput, getFs, getBasename, and getPath from src/utils/io.
• Updated the following validators to use the IO helpers: dotValidator, obfsetValidator, astericsValidator, applePanelsValidator, snapValidator, opmlValidator, excelValidator, and touchChatValidator.
• Updated the validation entrypoint validateFileOrBuffer in src/validation/index.ts to use getBasename, readBinaryFromInput, and getFs for consistent name resolution and file reads when a path is provided.
• Preserved existing behavior and validator logic while making file access conditional on the shared IO layer so browser builds won't import Node fs/path at module load time.

Testing

• No automated tests were run as part of this change.

---

Codex Task

[codecov-commenter]

Welcome to Codecov 🎉

Once you merge this PR into your default branch, you're all set! Codecov will compare coverage reports and display results in all future pull requests.

ℹ️ You can also turn on project coverage checks and project coverage reporting on Pull Request comment

Thanks for integrating Codecov - We've got you covered ☂️